Undersea cables are used to transmit electrical power and signals to great depths for numerous undersea applications including offshore oil wellheads, robotic vehicle operation, submarine power transfer and fiber optic cables. Submersible cables for underwater transmission of electrical power are known, for example, U.S. Pat. No. 4,345,112 (Sugata et al.), and U.S. Pat. App. Pub. No. 2007/0044992 (Bremnes). Such submersible power transmission cables generally include conducting elements and load bearing elements that are generally required to be able to fully withstand, without breaking, their drawing-out and winding-up by a capstan as the cable is deployed and retrieved from a vessel at the sea surface or underwater. Greater working depths are generally desired; however, the maximum working depth of a cable is generally limited by the maximum load and strain the cable can withstand under its own weight. The maximum depth and power transfer capability is thus limited by the material properties of the conducting elements and load bearing elements.
Submersible power transmission cables are normally manufactured using metal (e.g., steel, copper, aluminum) conductor wires and/or load bearing elements, and generally have substantial transverse cross sections, thereby providing the cable with considerable added weight due to the high specific gravity of metals, and copper in particular. Furthermore, because copper wires generally have a poor load bearing capacity, the water depth at which submersible power transmission cables incorporating copper conductors can be used is somewhat limited. Various cable designs have been proposed to achieve the high tensile strength and break resistance needed to successfully deploy underwater cables over long distances and depths (e.g., lengths of 1,000 meters or longer), as exemplified by U.S. Pat. App. Pub. Nos. 2007/0271897 (Hanna et al.); 2007/0237469 (Espen); and U.S. Pat. App. Pub. Nos. 2006/0137880, 2007/0205009, and 2007/0253778 (all Figenschou). For some deep water applications, unarmored cables have been constructed using, for example, KEVLAR and copper. Nevertheless, a lightweight, high tensile strength power umbilical or tether capable of transmitting large quantities of electrical power, fluids and electric current/signals between equipment located at the sea surface and equipment located on the sea bed, particularly in deep waters, continues to be sought.